Flywheel - Clutch Basics

1/8You need all the horsepower the engine can handle. You need to be certain you're not losing it through the inefficiency of the clutch package.

When you pay good money for horse-power, you want that power to go to the wheels as planned. Cars with manual transmission have a virtual Twilight Zone of variables, so to speak, that can rob you of those hard-earned horses. A car's flywheel, clutch, pressure plate, and, yes, even the throwout bearing, can be one of many complex problems. As the mechanism for transferring the engine's revolutions to the transmission, there are always opportunities for loss. That loss can happen when you are in a restart or other critical times on the track. There's never any insurance against blowing a restart, but you can try to make sure your equipment is not the cause.

With so many different types of cars racing under different rules, the amount of information on these components would quickly fill the pages of this magazine. Taking the time to ensure your clutch assembly is put together right and utilizes the right components can be complicated, so you need to know about clutches and their respective components. Remember, there is no "off the shelf" system for your application. Also, because knowledge is power, the best tip we know is to call the tech line of a supplier to get the perfect application for your needs. It helps to have a little background before you make that call.

General Tips* The ring gear flywheel size determines your clutch size, 1011/42 or 11 inches. The flywheel has to fit within the bolt circle of the crank and match up to the pressure plate. It's only one part of a system. If you remember that, you'll make fewer trips back to the parts store for the right pieces.

2/8Here's a trick setup. An aluminum button flywheel for a 711/44-inch mini disc assembly is bolted onto an automatic's flexplate. This gives the benefit of lightweight components and less rotating mass. The unit still matches up to a starter.

* Should you use a steel or aluminum flywheel? Generally, when you run a higher rpm (6,500 and up), you'll need an aluminum flywheel. Less reciprocating weight and less spinning mass equals higher recovery rate, or the time it takes to get both the flywheel and your tranny up to matching speeds. For comparison, here are some weights to remember: stock Chevy flywheel-25 pounds; steel aftermarket, SFI approved-25-40 pounds; aluminum aftermarket-15 pounds.

* If you're running a Street Stock or some form of heavy car, you'll need more torque to move its weight. A steel flywheel can help. The same holds true for classes with engines that don't turn the higher rpm (less than 6,500). If your class has a cam rule limiting your engine to a 440-460 lift cam, you can use the steel flywheel.

* On the other end of the scale, cheater pressure plates-made especially for circle track-weigh only 12 pounds, or roughly half of a normal pressure plate's weight. They're made for rules that stipulate use of a stock-appearing pressure plate. Couple this with a 15-pound flywheel and you shave off quite a bit of reciprocating weight. These components are made for higher-revving motors, so more of what you've paid for reaches the rear wheels.

3/8Here's a lightweight aluminum flywheel with an insert wear piece. These are good investments as both the starting gear ring and wear piece can be rebuilt. Note the holes to shave off weight.

* If you're looking for a standard configuration aluminum flywheel that can hold up to the rigors of racing, there are some available that use friction materials consisting of bronze and iron. The different material allows for better contact between the clutch disc and flywheel while the aluminum saves weight. Those contact areas can be replaced when needed.

* Throwout bearings require an air gap between the bearings and the pressure plate. The recommended size is usually 31/416-11/44 inch, but the gap will depend on the style of clutch. If it's not spaced properly, it will hang up. We all know what can happen to an engine when a shift is missed. This clearance is even more critical on the longer styles. The wrong gap will wear out the bearing faster and take other parts with it.

4/8A pilot tool is great for perfect, easy alignment of the clutch disc. It should match up to both the spline and the tip's diameter and length to fit correctly.

* A throwout bearing can be installed backwards. To install correctly, the larger end goes to the front or pressure plate, the smaller end toward the rear. Also, the clutch fork fingers must be located properly on the wear surface to be installed properly.

* Check the spring clip on the clutch fork where it holds the throwout bearing. Make sure it's working before you install it. They sometimes break off or bend out of position.

* Adjust the clutch fork to work in the center of its range. Adjust the clutch linkage if it's mechanical. With hydraulic clutches, check for any possible binding. The idea is for the entire assembly to function smoothly and consistently without binding.

* If you're having trouble lining up the clutch fork, there is an adjustable clutch fork pivot ball available. It can adjust 151/416-1111/416 inches.

* If you've bent the clutch linkage, there are replacement units available made from heat-treated, 4140 chrome steel.

5/8Even within one manufacturer, there are different grades of a product, in this case noted by color. The black ones are truck clutches, the orange is better than OEM, and the yellow and gold are race quality.

* Use only approved fasteners when mounting the flywheel to the crank and the pressure plate to the flywheel. The same holds true for automatics and mounting flexplates. Always check the length of the bolts so they don't bottom out. Use the crisscross method of tightening, and they'll need to be torqued. Also, do a rotation check so they don't impact the block after they pass through the crank.

* If you have a damaged ring gear, it can usually be replaced. Manufacturers sell replacement ring gears that fit both steel and aluminum units.

* Make sure the new clutch disc is installed correctly. It has an offset. If it is in backwards, it will bend and run out of balance. It could take the pressure plate with it when it goes, too. Always make sure the sprung center of the disc is facing away from the flywheel.

* A pilot tool is a good thing to have. You can make one from the input shaft of a broken tranny or buy a metal or plastic one locally. There are many different sizes out there. The spline and the length and diameter of the tip have to match. Clutch kits usually come with pilot tools. Always use the tool instead of your tranny to line up the components.

Using OEM Parts* On stock cast-iron flywheels, small heat cracks often appear on the surface. It is normal unless they extend to the center of the recess, in which case it's junk and you need to get it off the car.

* On Fords it is advisable to beef up the bellcrank with some triangulation. Welding on some reinforcement can help this piece work better under higher pressure. Take the piece off the car and wash out the grease. Blast the part, inspect for cracks, and weld on the extra reinforcement. Paint the part, install it into the car, grease it, and you're done.

* Certain engines come with a counterweight in the flywheel to compensate for the lack of counterweight in the crankshaft. This is known as Detroit balance, and those parts usually have a different listing in the catalogs. Make sure you know if yours has such a weight.

* For all types of cars, using a simple stud kit for attaching the pressure plate has benefits. It's easier overall. Put the clutch disc in place with the pilot/spline tool. Hang the pressure plate on studs and you won't have to hold up a heavy steel pressure plate while working the bolts into the flywheel. If you mess up the threads on the studs, the flywheel is still good. It makes good sense, considering how inexpensive a stud kit can be.

7/8If your high-performance aluminum flywheel has a contact patch that's used up, a new one can be installed relatively easy. The same holds true for the gear ring around the flywheel.

Musts And NeversMust: Clean your hands before installing or even handling the clutch disc to prevent contamination of the fiber surface. After you clean your hands, clean the surfaces before installing the clutch disc. The same holds true for the pressure plate and its mating surface. It's made of metal so dirt and grease won't absorb like the clutch, but any contaminants on the surface will get pushed into the clutch material. Use a good solvent and dry all parts.

Must: Make sure the style matches when replacing throwout bearings. Mate Borg and Beck pieces with Borg and Beck, long style with long style, and so on. Double check when you buy it and keep all the parts together. You could mix them up with the clutch from your tow vehicle or another project.

Must: Always check your pilot bearing for play and/or excessive wear. The one-piece, non-roller units are hard to check for wear. For as little as they cost, buy them by the handful and you'll always be sure by changing them out. Also, is it time for you to upgrade to a roller pilot bearing?

Must: When installing a new disc and pressure plate, use a new flywheel or at least have the old one resurfaced. New metal making contact with seasoned or used metal is asking for trouble. Also, always use a new disc with a new pressure plate.

8/8The clutch fork in your system is exposed to massive workloads. Make sure yours is up to the task with a performance model, even if your system is mostly stock.

Must: Always use the correct hardware-flywheel bolts for standard and automatic transmissions are different. Flywheel bolts are usually longer as flywheels are thicker than flexplates. But if the bolts are too long, they'll hit the block and stop rotation.

Must: Use only flat washers with cap screws on aluminum flywheels. Lock, star, or any other washer types can gall and scrape the aluminum.

Must: Use the threadlockers. You don't want any of them coming loose. Make sure you've got the right strength threadlocker. Some require heat to remove.

Must: Always torque correctly51/416-18x1-inch bolts to 25-30 ft-lb;31/48-16x1-inch bolts to 30-40 ft-lb;71/416-20x1-inch bolts to 70-80 ft-lb;11/42-20x1-inch bolts to 100-110 ft-lb.Make sure your torque wrench is accurate.Must: Check your motor and transmission for oil leaks. They can contaminate the clutch material and severely affect the performance and life of the system. The same holds for a hydraulic clutch.

Never: Weld on the clutch lever to balance a pressure plate to a flywheel. It can weaken the molecular structure of the metal and ultimately break. Instead, remove metal from the flywheel where necessary.

Never: Use the transmission and its input shaft to line up the clutch disc. The weight of the transmission can bend the metal center disc, affecting the balance of the clutch.

Never: Allow the clutch to wear below a compressed thickness of 0.280 inch. You're asking for trouble, and slipping is the least of it.

Tow VehiclesDid you know that car and truck clutches are different? Truck clutches have 10-12 percent more grip. Aftermarket truck clutches usually have a higher clamp load than OEM units. They use a better coefficient of friction material or a more aggressive friction material. Truck units are heavier and larger than car versions. The shudder frequency, or that jerking until the clutch is completely engaged, is reduced by the small springs on the clutch disc. The higher number of springs means a tougher clutch. Most truck kits include a spline tool and throwout bearing. Some offer a pressure ring for heavy-duty towing.